1. Field of the Invention
The present invention relates to an industrial diamond coating and a method of manufacturing the same.
2. Description of the Prior Art
The life time of machine tools such as cutting tools and grinding tools or other instruments having very hard surfaces or abrasive edges for machining purpose can be prolonged by coating, directly on the hard surfaces or abrasive edges, protection films made of very hard materials such as diamond, titanium carbide, titanium nitride, carbonated titanium nitride, aluminum oxide. Particularly, diamond coating has been believed to be very effective in the cases of coating on surfaces made of nonferrous metals or ceramics.
One of the practical problems of these technique is the coming-off or rubbing-off of the diamond film from the surface of a tool. Until now, there has not been yet accomplished sufficient adhesivity of diamond coatings to the surfaces of tools. The difference in thermal expansion coefficient between the diamond film and the underlying surfaces has been considered as a cause of separation of the diamond films from the surface.
The applicant has proposed an improved method for dealing with the above conventional shortcoming in a Japanese patent application Ser. No. 2-76308 filed on Mar. 26, 1990. FIGS. 1(A) to 1(C) are cross sectional views showing a method of forming a diamond coating in accordance with the invention proposed by the Japanese application. FIG. 1(A) is a diagram showing a cross sectional view of the diamond crystals grown from a substrate 1 in the form of a thin film as designated by numeral 10. As shown in the figure, the crystals are grown in inverted conical shapes. The contact areas of the crystals to the underlying surface of the substrate are very small because of the inversion of the cones, resulting in poor adhesivity. The substrate 1 coated with the diamond film 10 is then joined to the surface of an object 20 to be reinforced by the diamond film by means of a gold solder 11 as shown in FIG. 1(B). Finally, the substrate 1 is eliminated from the diamond film 10 by mechanical grinding as shown in FIG. 1(C).
As easily understood from FIG. 1(C), the contact areas of the diamond crystals 10 and the surface of the object 20 are substantially increased by this procedure so that mechanical strength of the coating structure can be greatly improved, resulting also from the effects of the adhesive. Accordingly, this method is very effective in many applications. On the other hand, some inconveniences, however, have arisen when the above method is applied to devices which produce much frictional heat during machining such as in the cases of some grinding tools. Diamond coating formed on a substrate was rubbing off from the surface of the substrate in those cases.